Adaptive Beamforming Scanning

ABSTRACT

There is provided mechanisms for adaptive beamforming scanning. A method is performed by a network device having a non-uniform directional network coverage. The method comprises obtaining a beam pattern indicating spatial directions in which reception of identification signals is to be scanned, wherein the beam pattern is defined by the non-uniform directional network coverage. The method comprises scanning with directional beams in the spatial directions according to the beam pattern for reception of the identification signals from wireless devices

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/524,157 filed 3 May 2017, which is a U.S. National Phase ApplicationNo. PCT/CN2015/091419 filed 2 Oct. 2015. The entire contents of eachaforementioned application is incorporated herein by reference.

TECHNICAL FIELD

Embodiments presented herein relate to adaptive beamforming scanning,and particularly to a method, a network device, a computer program, anda computer program product for adaptive beamforming scanning.

BACKGROUND

In communications systems, there may be a challenge to obtain goodperformance and capacity for a given communications protocol, itsparameters and the physical environment in which the communicationssystem is deployed.

For example, basic requirement for any cellular communications system isthe possibility for a wireless device to initially request a connectionsetup, commonly referred to as random access. In Long Term Evolution(LTE) communications systems, the random access procedure comes in twoforms, allowing the random access to be either contention-based orcontention-free. The contention-based procedure comprises four-steps; afirst step of preamble transmission, a second step of random accessresponse, a third step of protocol Layer 2/ Layer 3 messagetransmission, and a fourth step of contention resolution messageexchange.

In LTE, the preamble sequences in the first step are generated fromcyclic shifts of a root Zadoff-Chu (ZC) sequence. Sequences obtainedfrom cyclic shifts of different ZC sequences are not orthogonal.Therefore, orthogonal sequences obtained by cyclically shifting a singleroot sequence should be favored over non-orthogonal sequences. Thepreamble sequence is by the wireless device sent in a time-frequencyslot towards a radio access network node in the communication system.

Once detecting the preamble in the time-frequency slot, the radio accessnetwork node would in the second step send a Random Access Response(RAR) on the so-called Physical Downlink Shared CHannel (PDSCH), andaddressed by an identity (ID), Random Access Radio Network TemporaryIdentifier (RA-RNTI), which conveys the identity of the detectedpreamble, a timing alignment instruction to synchronize subsequentuplink transmission from the wireless device, an initial uplink resourcegrant for transmission of the message in the third step, and anassignment of a temporary Cell Radio Network Temporary Identifier(C-RNTI).

In the third step, the wireless device would convey the actual randomaccess procedure message, such as a radio resource control (RRC)connection request, tracking area update (TAU), or scheduling request.

In the fourth step, the contention resolution message would be sent bythe radio access network node.

It is foreseen that emerging wireless communications systems may benefitfrom the use of a large number of antenna elements at the radio accessnode (possibly also at the wireless device), especially in conjunctionwith higher carrier frequencies than used in current wirelesscommunications systems.

Hence, there is a need for an improved reception of identificationsignals from a wireless device.

SUMMARY

An object of embodiments herein is to provide efficient reception ofidentification signals from a wireless device.

According to a first aspect there is presented a method for adaptivebeamforming scanning. The method is performed by a network device havinga non-uniform directional network coverage. The method comprisesobtaining a beam pattern indicating spatial directions in whichreception of identification signals is to be scanned, wherein the beampattern is defined by the non-uniform directional network coverage. Themethod comprises scanning with directional beams in the spatialdirections according to the beam pattern for reception of theidentification signals from wireless devices.

Advantageously this method for adaptive beamforming scanning providesefficient beamforming scanning which enables efficient reception ofidentification signals from wireless devices.

Advantageously this method for adaptive beamforming scanning enablesregions in the network coverage having network outage to be avoided, orat least reduced.

Advantageously this method for adaptive beamforming scanning enablesbottlenecks which may occur in scenarios where identification signalsare to be received by a network device, such as during random accessprocedures, to be resolved, or at least reduced.

Advantageously, the disclosed scanning for reception of identificationsignals is transparent to the wireless devices, thus avoiding additionalsignaling complexity between network device and wireless device, furtheravoiding any change in the receiving algorithm at the wireless device,and thus allowing a wide applicability.

According to a second aspect there is presented a network device foradaptive beamforming scanning. The network device is configured for anon-uniform directional network coverage. The network device comprisesprocessing circuitry. The processing circuitry is configured to causethe network device to obtain a beam pattern indicating spatialdirections in which reception of identification signals is to bescanned, wherein the beam pattern is defined by the non-uniformdirectional network coverage. The processing circuitry is configured tocause the network device to scan with directional beams in the spatialdirections according to the beam pattern for reception of theidentification signals from wireless devices.

According to an embodiment the network device of the second aspectfurther comprises a storage medium. The processing circuitry isconfigured to retrieve a set of operations from the storage medium andto execute the set of operations in order for the network device toobtain the beam pattern and scan with the directional beams.

According to a third aspect there is presented a network device foradaptive beamforming scanning. The network device is configured for anon-uniform directional network coverage. The network node comprisesprocessing circuitry. The network node comprises a computer programproduct storing instructions that, when executed by the processingcircuitry, causes the network device to perform a method according tothe first aspect.

According to a fourth aspect there is presented a network device foradaptive beamforming scanning. The network device is configured for anon-uniform directional network coverage. The network node comprises anobtain module configured to obtain a beam pattern indicating spatialdirections in which reception of identification signals is to bescanned, wherein the beam pattern is defined by the non-uniformdirectional network coverage. The network node comprises a scan moduleconfigured to scan with directional beams in the spatial directionsaccording to the beam pattern for reception of the identificationsignals from wireless devices.

According to a fifth aspect there is presented a communications systemfor adaptive beamforming scanning. The system comprises circuitrydefining functionality of at least one network device according to anyof the second to fourth aspects.

According to a sixth aspect there is presented a computer program foradaptive beamforming scanning, the computer program comprising computerprogram code which, when run on a network device, causes the networkdevice to perform a method according to the first aspect.

According to a seventh aspect there is presented a computer programproduct comprising a computer program according to the sixth aspect anda computer readable medium, such as a non-volatile computer readablemedium, on which the computer program is stored.

It is to be noted that any feature of the first, second, third, fourth,fifth, sixth, and seventh aspects may be applied to any other aspect,wherever appropriate. Likewise, any advantage of the first aspect mayequally apply to the second, third, fourth, fifth, sixth, and/or seventhaspect, respectively, and vice versa. Other objectives, features andadvantages of the enclosed embodiments will be apparent from thefollowing detailed disclosure, from the attached dependent claims aswell as from the drawings.

Generally, all terms used in the claims are to be interpreted accordingto their ordinary meaning in the technical field, unless explicitlydefined otherwise herein. All references to “a/an/the element,apparatus, component, means, step, etc.” are to be interpreted openly asreferring to at least one instance of the element, apparatus, component,means, step, etc., unless explicitly stated otherwise. The steps of anymethod disclosed herein do not have to be performed in the exact orderdisclosed, unless explicitly stated.

BRIEF DESCRIPTION OF THE DRAWINGS

The inventive concept is now described, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram illustrating a communications systemaccording to embodiments;

FIG. 2a is a schematic diagram showing functional units of a networkdevice according to an embodiment;

FIG. 2b is a schematic diagram showing functional modules of a networkdevice according to an embodiment;

FIG. 3 shows one example of a computer program product comprisingcomputer readable means according to an embodiment;

FIGS. 4, 5, and 6 are flowcharts of methods according to embodiments;and

FIG. 7 schematically illustrates a beam pattern according toembodiments.

DETAILED DESCRIPTION

The inventive concept will now be described more fully hereinafter withreference to the accompanying drawings, in which certain embodiments ofthe inventive concept are shown. This inventive concept may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein; rather, these embodiments areprovided by way of example so that this disclosure will be thorough andcomplete, and will fully convey the scope of the inventive concept tothose skilled in the art. Like numbers refer to like elements throughoutthe description. Any step or feature illustrated by dashed lines shouldbe regarded as optional.

FIG. 1 is a schematic diagram illustrating a communications system 100where embodiments presented herein can be applied. The communicationssystem 100 comprises radio access network nodes 130, 130 a, 130 b, 130c, 130 d. Each radio access network node 130, 130 a, 130 b, 130 c, 130 dmay be a radio base station, a base transceiver station, a Node B, andEvolved node B, or an Access Point. Each radio access network node 130,130 a, 130 b, 130 c, 130 d is controlled by a respective network device200, 200 a, 200 b, 200 c, 200 d. The functionality of the network device200 will be further disclosed below. Further, the terms radio accessnetwork node and network device may be used interchangeably throughoutthis disclosure.

The radio access network nodes 130, 130 a, 130 b, 130 c, 130 d areconfigured for transmission and reception to and from wireless devices120 a, 120 b in directional beams. Each wireless device 120 a, 120 b maybe a portable wireless device, a mobile station, a mobile phone, ahandset, a wireless local loop phone, a User Equipment (UE), asmartphone, a laptop computer, a tablet computer, a wireless modem, or asensor.

As an example, radio access network node 130 is configured for suchtransmission and reception in directional beams 110 a, 110 b, 110 c, 110d. Thereby, a wireless device 120 a, 120 b located in a region definedby a directional beams 110 a, 110 b, 110 c, 110 d is able to access dataand services provided by the communications system 100. In theillustrative example of FIG. 1, wireless device 120 a is located in aregion served by directional beam 110 a of the radio access network node130 and wireless device 120 b is located in a region served bydirectional beam 110 b of the radio access network node 130.

In order for a wireless device 120 a, 120 b to access data and servicesprovided by the communications system 100 the wireless device 120 a, 120b establish an operative connection to at least one of the radio accessnetwork nodes 130, 130 a, 130 b, 130 c, 130 d. The process ofestablishing such an operative connection involves the wireless device120 a, 120 b to perform a random access procedure.

One example of a preamble sequence is constructed by repeating the shortpreamble sequence multiple times. In this way, the amount of specialrandom-access related processing and hardware support is significantlyreduced for multi-antenna systems, and the detector is also robustagainst inter-carrier interference from other uplink channels andsignals. Furthermore, the proposed preamble detector scheme can be usedin scenarios with a high amount of phase noise and frequency errors.

A radio access network node may commonly spatially scan its servingcoverage by hybrid beamforming switching (a combination of digital andanalogue beamforming) during the random access time window. In otherwords, a specific receiving beam usually stays at a certain slot, e.g.,1/N of the total preamble detection window length for a total of Ndirectional beams, before switching to another directional beam.

The shorter signal accumulation duration reduces the total receivedsignal power, and also the signal to noise and interference ratio of therandom access signal, and thus ultimately reduces the random accesssignal detection success rate and coverage region where the randomaccess signal can be received by the radio access network node. Thus, areceiving signal power gain obtained by massive antenna hybridbeamforming is reduced because of the short stay duration in eachdirectional beam as compared to a scenario where beam forming is notused.

A wireless device 120 a, 120 b may during its random access procedurethus repeatedly transmitting identification signals, such as a PhysicalRandom Access CHannel (PRACH) sequence, and the network device monitorsfor reception of the PRACH sequence in different directions byperforming scanning in directional beams. The coverage requirementscould be different in different directions of the network device 200owing to at least two reasons. Firstly, some neighboring network device200 a, 200 b, 200 c, 200 d may provide network access in a regioncovered by a directional beam of the network device 200. Secondly, theremight be compared to other directions, very few or even no requests atall from wireless devices 120 a, 120 b in a particular direction due toenvironmental factors, thus causing a comparatively very small presenceof wireless devices 120 a, 120 b in that particular direction. On thecontrary, in some other particular directions a good network coverage isnecessary due to neighboring network devices being far away in theseother particular directions. Therefore, a scanning procedure forreception of identification signals from wireless devices based on equaltime duration in each directional beam and with all directional beamshaving equal widths cannot match communications systems 100 withnon-uniform network coverage.

The embodiments disclosed herein therefore relate to adaptivebeamforming scanning. In order to obtain adaptive beamforming scanningthere is provided a network device 200, a method performed by thenetwork device 200, a computer program comprising code, for example inthe form of a computer program product, that when run on a networkdevice 200, causes the network device 200 to perform the method.

FIG. 2a schematically illustrates, in terms of a number of functionalunits, the components of a network device 200 according to anembodiment. Processing circuitry 210 is provided using any combinationof one or more of a suitable central processing unit (CPU),multiprocessor, microcontroller, digital signal processor (DSP),application specific integrated circuit (ASIC), field programmable gatearrays (FPGA) etc., capable of executing software instructions stored ina computer program product 310 (as in FIG. 3), e.g. in the form of astorage medium 230.

Particularly, the processing circuitry 210 is configured to cause thenetwork device 200 to perform a set of operations, or steps, S102-S208.These operations, or steps, S102-S208 depicted in FIGS. 4, 5 and 6 willbe disclosed below. For example, the storage medium 230 may store theset of operations, and the processing circuitry 210 may be configured toretrieve the set of operations from the storage medium 230 to cause thenetwork device 200 to perform the set of operations. The set ofoperations may be provided as a set of executable instructions.

Thus, the processing circuitry 210 is thereby arranged to executemethods as herein disclosed. The storage medium 230 may also comprisepersistent storage, which, for example, can be any single one orcombination of magnetic memory, optical memory, solid state memory oreven remotely mounted memory. The network device 200 may furthercomprise a communications interface 220 for communications with at leastone wireless device 120 a, 120 b and possible at least one other networkdevice 200 a, 200 b, 200 c, 200 d. As such the communications interface220 may comprise one or more transmitters and receivers, comprisinganalogue and digital components. The processing circuitry 210 controlsthe general operation of the network device 200 e.g. by sending data andcontrol signals to the communications interface 220 and the storagemedium 230, by receiving data and reports from the communicationsinterface 220, and by retrieving data and instructions from the storagemedium 230. Other components, as well as the related functionality, ofthe network device 200 are omitted in order not to obscure the conceptspresented herein.

FIG. 2b schematically illustrates, in terms of a number of functionalmodules, the components of a network device 200 according to anembodiment. The network device 200 of FIG. 2b comprises a number offunctional modules; an obtain module 210 a configured to perform belowsteps S102, S104, and a scan module 210 b configured to perform belowstep S112. The network device 200 of FIG. 2b may further comprises anumber of optional functional modules, such as any of an update module210 c configured to perform below steps S106, S108, S108 b, S110, andidentify module 210 d configured to perform below step S108 a, a mergemodule 210 e configured to perform below step S108 c, and a split module210 f configured to perform below step S108 d. The functionality of eachfunctional module 210 a-210 f will be further disclosed below in thecontext of which the functional modules 210 a-210 f may be used. Ingeneral terms, each functional module 210 a-210 f may in one embodimentbe implemented only in hardware or and in another embodiment with thehelp of software, i.e., the latter embodiment having computer programinstructions stored on the storage medium 230 which when run on theprocessing circuitry makes the network device 200 perform thecorresponding steps mentioned above in conjunction with FIG. 2b . For ahardware implementation the functional modules 210 a-210 f may beimplemented in the processing circuitry 210, possibly also in thecommunications interface 220 and the storage medium 230. It should alsobe mentioned that even though the modules correspond to parts of acomputer program, they do not need to be separate modules therein, butthe way in which they are implemented in software is dependent on theprogramming language used. Preferably, one or more or all functional 210a-210 f may be implemented by the processing circuitry 210, possibly incooperation with functional units 220 and/or 230. The processingcircuitry 210 may thus be configured to from the storage medium 230fetch instructions as provided by a functional module 210 a-210 f and toexecute these instructions, thereby performing any steps as will bedisclosed hereinafter.

Hence, in comparison to FIG. 2a , FIG. 2b provides a functional orienteddescription of the network node 200 whereas FIG. 2a provides a buildingblock oriented view of the network node 200. The building blocks (i.e.,the processing circuitry 200, the communications interface 220, and thestorage medium 230) of the network node 200 in FIG. 2a may be configuredto perform the functionality defined by the functional modules 210 a-210f of the network node 200 in FIG. 2 b.

The network device 200 may be provided as a standalone device or as apart of at least one further device. For example, the network device 200may be provided in a node of a radio access network or in a node of acore network. Alternatively, functionality of the network device 200 maybe distributed between at least two devices, or nodes. These at leasttwo nodes, or devices, may either be part of the same network part (suchas the radio access network or the core network) or may be spreadbetween at least two such network parts. In general terms, instructionsthat are required to be performed in real time may be performed in adevice, or node, operatively closer to the wireless devices 120 a, 120 bthan instructions that are not required to be performed in real time.

Thus, a first portion of the instructions performed by the networkdevice 200 may be executed in a first device, and a second portion ofthe of the instructions performed by the network device 200 may beexecuted in a second device; the herein disclosed embodiments are notlimited to any particular number of devices on which the instructionsperformed by the network device 200 may be executed. Hence, the methodsaccording to the herein disclosed embodiments are suitable to beperformed by a network device 200 residing in a cloud computationalenvironment. Therefore, although a single processing circuitry 210 isillustrated in FIG. 2a the processing circuitry 210 may be distributedamong a plurality of devices, or nodes. The same applies to thefunctional modules 210 a-210 f of FIG. 2b and the computer program 320of FIG. 3 (see below).

FIG. 3 shows one example of a computer program product 310 comprisingcomputer readable means 330. On this computer readable means 330, acomputer program 320 can be stored, which computer program 320 can causethe processing circuitry 210 and thereto operatively coupled entitiesand devices, such as the communications interface 220 and the storagemedium 230, to execute methods according to embodiments describedherein. The computer program 320 and/or computer program product 310 maythus provide means for performing any steps as herein disclosed.

In the example of FIG. 3, the computer program product 310 isillustrated as an optical disc, such as a CD (compact disc) or a DVD(digital versatile disc) or a Blu-Ray disc. The computer program product310 could also be embodied as a memory, such as a random access memory(RAM), a read-only memory (ROM), an erasable programmable read-onlymemory (EPROM), or an electrically erasable programmable read-onlymemory (EEPROM) and more particularly as a non-volatile storage mediumof a device in an external memory such as a USB (Universal Serial Bus)memory or a Flash memory, such as a compact Flash memory. Thus, whilethe computer program 320 is here schematically shown as a track on thedepicted optical disk, the computer program 320 can be stored in any waywhich is suitable for the computer program product 310.

FIGS. 4 and 5 are flow chart illustrating embodiments of methods foradaptive beamforming scanning. The methods are performed by the networkdevice 200. The methods are advantageously provided as computer programs320.

Reference is now made to FIG. 4 illustrating a method for adaptivebeamforming scanning as performed by the network device 200 according toan embodiment.

The network device 200 has a non-uniform directional network coverage.In general terms, network coverage of a network device 200 may bedefined as the region in which the network device 200 can providenetwork access to a wireless device 120 a, 120 b. Network access interalia involves the network device to receive identification signals fromthe wireless device 120 a, 120 b.

As noted above, the wireless devices 120 a, 120 b perform a randomaccess procedure in order to obtain network access. This random accessprocedure involves the wireless devices 120 a, 120 b to transmitidentification signals. The network device 200 therefore performsscanning for reception of the identification signals. The scanning isperformed according to a beam pattern.

The network device 200 is therefore configured to, in a step S102,obtain a beam pattern. In this respect the obtain module 210 a maycomprise instructions that when executed by the network device 200causes the processing circuitry 210, possibly in conjunction with thecommunications interface 220 and the storage medium 230, to obtain thebeam pattern in order for the network device 200 to perform step S102.Examples of how the beam pattern may be obtained will be disclosedbelow. The beam pattern indicates spatial directions in which receptionof identification signals is to be scanned. The beam pattern is definedby the non-uniform directional network coverage of the network device200. Examples of how the beam pattern may be defined by the non-uniformdirectional network coverage will be disclosed below.

Once the beam pattern has been obtained the network device 200 can usethe beam pattern for the scanning for reception of the identificationsignals. The network device 200 is configured to, in a step S112, scanwith directional beams 110 a, 110 b, 110 c, 110 d in the spatialdirections according to the beam pattern for reception of theidentification signals from wireless devices 120 a, 120 b. In thisrespect the scan module 210 b may comprise instructions that whenexecuted by the network device 200 causes the processing circuitry 210,possibly in conjunction with the communications interface 220 and thestorage medium 230, to scan with directional beams 110 a, 110 b, 110 c,110 d in order for the network device 200 to perform step S112.

This method for adaptive beamforming scanning enables a conditional(i.e., conditional on the non-uniform network coverage) unequal-timeduration beam scanning procedure for reception of identification signalsto match coverage demand in different directions of the network device200. Thereby, instead of equal time-spatial beam scanning for receptionof identification signals, this method for adaptive beamforming scanningenables the coverage of the directional beams to match the non-uniformdirectional network coverage in the different scanning directions.

The herein disclosed beam scanning procedure could thereby boost thereceived signal quality adaptively so as to mitigate any bottleneckcaused by random access attempts made in certain regions of the networkcoverage of the network device 200.

Embodiments relating to further details of adaptive beamforming scanningwill now be disclosed.

There may be different occasions when the network device 200 is toperform the scanning for reception of the identification signals as instep S112. For example, the identification signals may be part of arandom access procedure. Hence, the scanning for reception of theidentification signals may be part of a random access procedure.

Further, there may be different types of identification signals to scanfor. For example, each identification signal may comprise a physicalrandom access channel (PRACH) preamble. That is, the identificationsignals may be random access preamble signals, constructed by a numberof repeated short preambles.

There may be different ways define the non-uniform spatial networkcoverage. For example, the non-uniform spatial network coverage mayidentify at least two network coverage regions having mutually differentnetwork coverage levels. Hence, the non-uniform spatial network coveragemay comprise at least on region having a lower network coverage thananother region in the non-uniform spatial network coverage. As theskilled person would understand, the herein disclosed embodiments arenot limited to any particular number of coverage levels in thenon-uniform spatial network coverage.

All directional beams 110 a, 110 b, 110 c, 110 d have a certain beamwidth. There may be different ways to determine the values of these beamwidths. The directional beams 110 a, 110 b, 110 c, 110 d may have beamwidth values taken from a non-uniform set determined according to thebeam pattern. Hence, the directional beams 110 a, 110 b, 110 c, 110 dmay have non-uniform beam widths, or lobes. However, in order tominimize the risk of network coverage holes, the directional beams 110a, 110 b, 110 c, 110 d may be required to be wider or equal than acertain minimum beam width. Hence, none of the beam width values may besmaller than a pre-configured first threshold value.

The scanning remains in each directional beam 110 a, 110 b, 110 c, 110 da certain amount of time. For example, the directional beams 110 a, 110b, 110 c, 110 d may take time duration values for the scanning from anon-uniform set of time duration values, where the non-uniform set oftime duration values is determined according to the beam pattern.However, in order to minimize the risk of network coverage holes, thescanning may be required to stay in each directional beam 110 a, 110 b,110 c, 110 d equal or longer than a certain minimum stay time. Hence,none of the time duration values may be smaller than a pre-configuredsecond threshold value. In this respect, the network node 200 canfurther be configured to receive identification signals in at least twofrequency regions in each directional beam 110 a, 110 b, 110 c, 110 d.In other words, the network node 200 may scan for reception ofidentification signals in at least two different frequency spectra usinga single directional beam in a single direction.

Mechanisms to determine the time duration values may be based on linearequations with parameters defining the time duration proportions betweenthe directional beam 110 a, 110 b, 110 c, 110 d with a summation to be1.

Different examples for determining the coefficients representing thetime duration values will be disclosed next.

According to a first example, a constraint relation is defined asfollows. Set 1=Σ_(k=0) ^(n)x^([k])a^([k]), for a total of n directionalbeams and x^([k]) being the stay duration proportion for directionalbeam k, and a^([k]) being the corresponding coefficient.

According to a second example, set a^([k]):a^([k+1])=Q_(edge,k):Q_(edge,k+1), where Q_(edge,k) is the edge quality(e.g. measured as signal strength, signal power, signal to interferenceand noise ratio (SINR), signal to noise ratio SNR, etc.) of directionalbeam k.

According to a third example, a non-linear relation, such as 1=Σ_(k=0)^(n)f(x^([k]))a^([k]) is used, where f (y) is a non-linear function withinput argument y.

Furthermore, the total scanning duration can also be re-configuredexplicitly via a parameter or implicitly via the default scanningpattern. That is, according to an embodiment the total time duration forscanning through all directional beams 110 a, 110 b, 110 c, 110 d istime-varying and determined according to the beam pattern. The totalduration of the scanning can thereby be adapted according to thecoverage requirement of the network device 200.

According to an embodiment the beam pattern is defined such that adirectional beam pointing in a direction of a first network coverage isto have a wider width and/or lower time duration than a directional beampointing in a direction of a second network coverage being lower thanthe first network coverage.

Thereby, instead of spending equal time duration in each directionalbeam for scanning in different directions, the time duration for anydirectional beam covering regions with poor network coverage can beincreased whilst the time duration for any directional beam coveringregions with good network coverage can be reduced. This allows thescanning to spend more time in the directional beam covering regionswith poor network coverage than in the directional beam covering regionswith good network coverage, thereby allowing a larger portion of thetotal time for the scanning to be spent where needed the most (i.e., inthe directional beam covering regions with poor network coverage).

Further thereby, instead of equal widths of all directional beams, thewidth of any directional beam covering regions with poor networkcoverage can be narrowed to increase the beamforming gain and such thatregions with poor network coverage can be scanned by multiple narrowdirectional beams whilst the width of any directional beam coveringregions with good network coverage can be widened so as to monitor awider region.

Reference is now made to FIG. 5 illustrating methods for adaptivebeamforming scanning as performed by the network device 200 according tofurther embodiments.

There may be different ways for the network device 200 to determine andupdate the beam pattern. Parallel reference is initially also made tothe flow chart of FIG. 6 illustrating an embodiment for updating thebeam pattern.

The network device 200, in a step S202, obtains enough measurements todetermine the coverage difference between each directional beam. One wayto implement step S202 is to perform step S104. The network device 200,in a step S204, evaluates the coverage differences (e.g. proportional tothe coverage requirement) between different directions (i.e.corresponding to different directional beams. One way to implement stepS204 is to perform step S106. The network device 200, in a step S206,determines the beam pattern based on the coverage differences inaccordance with other embodiments as disclosed herein. One way toimplement step S206 is to perform step S108. Once the beam pattern hasbeen determined as in step S206, new measurement information may beobtained in a new occurrence of step S202, as indicated by the feedbackstep S208. An updated coverage difference may then be determined basedon the thus new measurement information and an updated beam pattern maybe determined based on the thus updated coverage difference.

Each of the steps S202, S204, and S206 will now be disclosed in moredetail. In general terms, as noted above, steps S202, S204, and S206 maybe implemented by the network device 200 performing steps S104, S106,and S108, respectively.

Details of step S202 will now be disclosed. Particularly, according toan embodiment the network device 200 is configured to, in a step S104,obtain measurement information from the wireless devices 120 a, 120 b.There are different kinds of measurement information the network device200 may obtain from the wireless devices 120 a, 120 b. For example, themeasurement information may be indicative of handover measurements,measurement on camped on directional beams 110 a, 110 b,110 c, 110 d,pilot signal quantities, number of failed random access attempts made bythe wireless devices 120 a, 120 b, or any combination thereof.Measurement reports of handover events may thereby be obtained by thenetwork device 200. Specifically, when a wireless device 120 a, 120 b ishanded over to another network device, the serving network device priorto handover may record the directional beam on which the wireless device120 a, 120 b is camping on before handover and the corresponding lastpilot signal quality report from the wireless device. The new servingnetwork device after handover can immediately configure the handed overwireless device 120 a, 120 b to report the new camped on directionalbeam and the corresponding pilot signal qualities of the new servingnetwork device. After initial random access, the network device canconfigure the wireless device 120 a, 120 b to report the camped ondirectional beam and the corresponding pilot signal quality of theserving network device and, optionally, also to report any directionalbeams and the corresponding pilot signal qualities of neighboringnetwork devices.

Details of step S204 will now be disclosed. After having obtained themeasurement information the network device 200 may identify coveragedifferences between different regions of its non-uniform directionalnetwork coverage. The network device 200 may thus be configured to, in astep S106, update the non-uniform directional network coverage accordingto the measurement information. In more detail, the network device maybe configured to determine the pilot signal qualities at the beamcoverage edge. For instance, the beam coverage edge of a particulardirectional beam can be determined according to the worst qualityreported by a wireless device 120 a, 120 b when the wireless device 120a, 12b newly accesses or leaves this particular directional beam. Thenetwork device 200 may thereby be configured to rank the directionalbeams according to the edge quality.

Details of step S206 will now be disclosed. The network device 200 maybe configured to, in a step S108, update the beam pattern according tothe updated non-uniform directional network coverage and based thereonupdate the beam pattern. Particular embodiments disclosing how thenetwork device 200 may update the beam pattern will be disclosed belowin relation to steps S108 a, S108 b, S108 c, and S108 d. Theseembodiments involve the beam pattern to be adjusted in time and/or spaceaccording to the measurement information obtained in step S104.

An embodiment for updating the beam pattern involves the network device200 to be configured to, in a step S108 a, identify which directionalbeam 110 a, 110 b, 110 c, 110 d of the directional beams 110 a, 110 b,110 c, 110 d that corresponds to which measurement information.According to this embodiment the network device 200 is furtherconfigured to, in a step S108 b, update at least one of a beam widthvalue and a time duration value of the directional beams 110 a, 110 b,110 c, 110 d according to the measurement information of the respectivedirectional beam 110 a, 110 b, 110 c, 110 d.

As will be further disclosed below, updating the beam pattern maycomprise merging at least two neighbouring directional beams in the setof directional beams into one directional beam and/or splitting at leastone directional beam 110 a, 110 b, 110 c, 110 d in the set ofdirectional beams 110 a, 110 b, 110 c, 110 d into at least twodirectional beams. In order to do so, the network device 200 may beconfigured to, based on a set of directional beams from a default beampattern, estimate if the beam pattern results in over-dimensioned orunder-dimensioned directional beam coverage and, as a result thereof,determine adjusted directional beams so as to define an updated beampattern accordingly. Properties of the default beam pattern will bedisclosed below.

According to an embodiment, where the network device 200 is configuredwith a default set of directional beams, the network device 200 isconfigured to, in a step S108 c, merge at least two neighbouringdirectional beams in the set of directional beams into one directionalbeam. Merging neighbouring directional beams in the directions of goodnetwork coverage enables the scanning time to be increased in directionswith poor network coverage.

An example of a beam merging procedure will now be disclosed.

For a set of directional beams to be merged, the directional beam withthe worst edge quality within the set of directional beams isdetermined. The worst edge quality (denoted Q_(edge,min)) of thisdirectional beam is then determined and compared to a predeterminedminimum acceptable edge quality (denoted Q_(thres)) to obtain a beamdimension mismatch factor (denoted A) as follows:

Δ=Q _(edge,min) −Q _(thres)(dB)

The beam dimension mismatch factor is then converted from decibel scaleto linear scale using a function db2lin as follows:

m=db2lin(Δ)

Here, m represents the directional beam width adjustment. If m≥2 it ispossible for the directional beam with the worst edge quality to bemerged with an adjacent directional beam. Hence, the network device 200may be configured to use one widened directional beam instead of twoindividual (narrow) directional beams for reception of identificationsignals at such beam directions. The stay duration in this spatiallywidened (merged) directional beam could either remain as one scanningslot or be adjusted in accordance with embodiments disclosed hereinwhere the directional beams 110 a, 110 b, 110 c, 110 d take timeduration values for the scanning from a non-uniform set of time durationvalues.

According to an embodiment, where the network device 200 is configuredwith a default set of directional beams, the network device 200 isconfigured to, in a step S108 d, split at least one directional beam 110a, 110 b, 110 c, 110 d in the set of directional beams 110 a, 110 b, 110c, 110 d into at least two directional beams.

An example of a beam splitting procedure will now be disclosed.

For directional beam k, the dimension mismatch (denoted Δ_(k)) isdefined as

Δk=Q _(edge,k) −Q _(thres)(dB)

where Q_(thres) is the minimum acceptable edge quality and whereQ_(edge,k) is the edge quality for directional beam k.

The beam lobe width adjustment factor is then determined according to abeam dimension mismatch m_(k) for directional beam k according tofunction db2lin as follows:

m _(k) =db2lin(Δ_(k))

If m_(k)<1, directional beam k is under-dimensioned and its beam lobewidth is to be decreased (and the number of directional beams may beincreased due to directional beam k covers a narrower region). Thenetwork device 200 may be configured to use a subset of antenna elementsof the whole antenna array (possibly a “Port”) to generate an updateddirectional beam to replace a previously used directional beam generatedby the whole antenna array. The stay duration in each directional beamcould either remain as one scanning slot or be adjusted in accordancewith embodiments disclosed herein where the directional beams 110 a, 110b, 110 c, 110 d take time duration values for the scanning from anon-uniform set of time duration values.

The beam pattern originally used by the network device 200 may be adefault beam pattern. The default beam pattern may be hard-coded in thenetwork device 200, or obtained from another network device 200 a, 200b, 200 c, 200 d. In any initial beam scanning stage, or upon deploymentor installation of the network device 200, the default scanning patternmay be used. The default beam pattern may define equal time duration ineach directional beam 110 a, 110 b, 110 c, 110 d, and/or equal beamwidth of each directional beam 110 a, 110 b, 110 c, 110 d. That is, thedefault beam pattern may be defined such that all directional beams havethe same beam width and the stay time in each directional beam is equal.Alternatively, the default beam pattern may be defined such that thebeam widths and the stay times are set according to a defaultnon-uniform directional network coverage of the network device 200. Thenetwork device 200 may then be configured to, in a step S110, update thedefault beam pattern so as to obtain the updated beam pattern.

Once scanning with directional beams 110 a, 110 b, 110 c, 110 d in thespatial directions has occurred as in step S112, a new beam pattern maybe obtained in a new occurrence of step S102 and/or new measurementinformation may be obtained in a new occurrence of step S104, asindicated by the feedback steps S114, S116. New occurrences of stepsS106-S112 may then be performed based on the new beam pattern and/or thenew measurement information. However, as the skilled person understands,not all steps S104-S110 must be performed until the next occurrence ofstep S112. Which, if any, of steps S104-S110 to be performed dependinter alia on the measurement information made available to the networkdevice 200.

In general terms, the beam pattern is determined, updated, and adjustedso as to achieve optimized network coverage for the ensemble of wirelessdevices served by the network device 200. Hence, the beam pattern is notnecessarily determined, updated, or adjusted to optimize the networkcoverage for a specific wireless device or to optimize the initialaccess procedure of such a specific wireless device. In this respect,the operation cycle of determining, updating, and adjusting the beampattern may be regarded as quite long compared to the mobility controlcycles performed by the network device 200. In general terms, thedetermining, updating, and adjusting the beam pattern in the time orspace domain may therefore use long-term statistics of measurements; thelong-term statistics could represent statistics collected during minutesor hours, depending on the density change of wireless devices in thecommunications system 100 and traffic loading variation per specificdeployment of the network device 200. Hence the beam pattern may bedefined according to long-term statistics.

Particular reference is again made to the communications system 100 ofFIG. 1.

In this illustrative example, network device 200 a is closest to networkdevice 200; network device 1 is the second closest to network device200; and network device 200 d and 200 c are farthest to network device200. The service providing network coverages in different directionalbeams 110 a, 110 b, 110 c, 110 d are different due to the differentneighboring distances: directional beam 110 a takes the smallestcoverage; directional beam 110 b takes a larger coverage; anddirectional beam 110 d and 110 c take the similar largest coverage. Theresulting beam pattern 700, as determined according to embodimentsdisclosed herein, for this illustrative example is illustrated in FIG.7, in which the notation “Beam #x”, where x is 1, 2, 3, or 4, representswhich directional beam that is used by the network device 200 forscanning for reception of identification signals, as represented by theuser data in FIG. 7, from wireless devices 120 a, 120 b. Hence, inrelation to FIG. 1, Beam #1 may correspond to directional beam 110 b,Beam #2 may correspond to directional beam 110 d, Beam #3 may correspondto directional beam 110 c, and Beam #4 may correspond to directionalbeam 110 a. The duration in directional beam 110 a is the shortest andthe beam lobe width is largest; the duration in directional beam 110 bis longer and the beam lobe width is larger; duration in directionalbeams 110 d and 110 c take the longest duration and the beam lobe widthis the narrowest.

Advantageously the herein disclosed methods and network device 200 foradaptive beamforming scanning provides efficient beamforming scanningwhich enables efficient reception of identification signals fromwireless devices.

Advantageously the herein disclosed methods and network device 200 foradaptive beamforming scanning enables regions in the network coveragehaving network outage to be avoided, or at least reduced.

Advantageously the herein disclosed methods and network device 200 foradaptive beamforming scanning enables bottlenecks which may occur inscenarios where identification signals are to be received by a networkdevice, such as during random access procedures, to be resolved, or atleast reduced.

Advantageously, the disclosed scanning for reception of identificationsignals is transparent to the wireless devices, thus avoiding additionalsignaling complexity between network device and wireless device, furtheravoiding any change in the receiving algorithm at the wireless device,and thus allowing a wide applicability.

Advantageously the herein disclosed methods and network device 200 foradaptive beamforming scanning enables a conditional (i.e., conditionalon the non-uniform network coverage) unequal-time duration beam scanningprocedure for reception of identification signals to match coveragedemand in different directions of the network device 200. Thereby,instead of equal time-spatial beam scanning for reception ofidentification signals, this method for adaptive beamforming scanningenables the coverage of the directional beams to match the non-uniformdirectional network coverage in the different scanning directions.

Advantageously the herein disclosed methods and network device 200 foradaptive beamforming scanning could thereby be used to boost thereceived signal quality adaptively so as to mitigate any bottleneckcaused by random access attempts made in certain regions of the networkcoverage of the network device 200.

The inventive concept has mainly been described above with reference toa few embodiments. However, as is readily appreciated by a personskilled in the art, other embodiments than the ones disclosed above areequally possible within the scope of the inventive concept, as definedby the appended patent claims.

What is claimed is:
 1. A method of operation at a radio access node of acommunication network, the method comprising: determining differences innetwork coverage in two or more spatial directions relative to the radionetwork node; configuring a beam pattern in dependence on the determineddifferences in network coverage, including configuring non-uniform beamdurations and/or non-uniform beam shapes for two or more directionalbeams, wherein the non-uniformity accounts for the determineddifferences in network coverage; and scanning for random-accesssignaling incoming from given wireless devices, according to theconfigured beam pattern.
 2. The method of claim 1, further comprisingdetermining the differences in network coverage based on pilot-signalmeasurements obtained from given wireless devices operating atradio-coverage edges of the radio access node.
 3. The method of claim 2,wherein determining the differences in network coverage based onpilot-signal measurements comprises determining, for each of a pluralityof directions relative to the radio access node, a quality oravailability of radio coverage from one or more neighboring radio accessnodes at corresponding edges of radio coverage of the radio access node.4. The method of claim 1, wherein the radio access node uses a set ofdirectional beams for transmission and reception, and whereindetermining the differences in network coverage comprises evaluatingneighbor-node radio coverage at coverage edges of the respectivedirectional beams, based on downlink measurements made by wirelessdevices operating at the coverage edges of the respective beams.
 5. Themethod of claim 4, wherein the radio access node deems respective beamdirections or ranges of beam directions as corresponding to good networkcoverage or poor network coverage, in dependence on the evaluation ofneighbor-node radio coverage, and wherein configuring the beam patterncomprises configuring beams corresponding to good network coverage to bewider or shorter in duration than beams corresponding to poor networkcoverage.
 6. The method of claim 4, wherein the radio access node deemsrespective beam directions or ranges of beam directions as correspondingto good network coverage or poor network coverage, in dependence on theevaluation of neighbor-node radio coverage, and wherein configuring thebeam pattern comprises using a greater number of narrower beams to spandirectional ranges corresponding to poor network coverage, as comparedto the number of beams used to span directional ranges corresponding togood network coverage.
 7. A method of operation at a radio access nodeof a communication network, the method comprising: configuring a beampattern according to differences in network coverage in two or morespatial directions relative to the radio access node, wherein thedifferences in network coverage relate to an extent or quality ofoverlapping radio coverage as between the radio access node and one ormore neighboring radio access nodes, wherein the beam pattern defines aset of directional beams used by the radio access node for receptionbeamforming, and wherein configuring the beam pattern comprisesadjusting the set of directional beams, such that a non-uniformity inbeamforming gains among the directional beams reflects the differencesin network coverage; and scanning for incoming random-access signalingaccording to the configured beam pattern.
 8. The method of claim 7,wherein adjusting the set of directional beams includes configuringnon-uniform beam widths and/or beam durations within the set ofdirectional beams, and wherein narrower beam widths provide a higherbeamforming gain as compared to wider beam widths and longer beamdurations provide a higher beamforming gain as compared to shorter beamdurations.
 9. The method of claim 8, wherein adjusting the set ofdirectional beams comprises using wider-width or shorter-duration beamsin directions having good network coverage and using narrower-width orlonger-duration beams in directions not having good network coverage.10. A radio access node configured for operation in a communicationnetwork, the radio access node comprising: transceiver circuitryconfigured for reception beamforming using an associated plurality ofantennas or antenna elements; and processing circuitry operativelyassociated with the transceiver circuitry and configured to: determinedifferences in network coverage in two or more spatial directionsrelative to the radio network node; configure a beam pattern independence on the determined differences in network coverage, includingconfiguring non-uniform beam durations and/or non-uniform beam shapesfor two or more directional beams, wherein the non-uniformity accountsfor the determined differences in network coverage; and scan, using thetransceiver circuitry, for random-access signaling incoming from givenwireless devices, according to the configured beam pattern.
 11. Theradio access node of claim 10, wherein the processing circuitry isconfigured to determine the differences in network coverage based onpilot-signal measurements obtained from given wireless devices operatingat radio-coverage edges of the radio access node.
 12. The radio accessnode of claim 11, wherein the processing circuitry is configured todetermine the differences in network coverage based on pilot-signalmeasurements by determining, for each of a plurality of directionsrelative to the radio access node, a quality or availability of radiocoverage from one or more neighboring radio access nodes atcorresponding edges of radio coverage of the radio access node.
 13. Theradio access node of claim 10, wherein the radio access node uses a setof directional beams for transmission and reception, and wherein theprocessing circuitry is configured to determine the differences innetwork coverage by evaluating neighbor-node radio coverage at coverageedges of the respective directional beams, based on downlinkmeasurements made by wireless devices operating at the coverage edges ofthe respective beams.
 14. The radio access node of claim 13, wherein theprocessing circuitry is configured to deem respective beam directions orranges of beam directions as corresponding to good network coverage orpoor network coverage, in dependence on the evaluation of neighbor-noderadio coverage, and to configure the beam pattern by configuring beamscorresponding to good network coverage to be wider in shape or shorterin duration than beams corresponding to poor network coverage.
 15. Theradio access node of claim 13, wherein the processing circuitry isconfigured to deem respective beam directions or ranges of beamdirections as corresponding to good network coverage or poor networkcoverage, in dependence on the evaluation of neighbor-node radiocoverage, and to configure the beam pattern by using a greater number ofnarrower beams to span directional ranges corresponding to poor networkcoverage, as compared to the number of beams used to span directionalranges corresponding to good network coverage.